Many types of computing and/or communications devices are capable of providing a wide array of functions while the devices move from place to place. These devices will be generically referenced herein as “mobile devices”. For a variety of reasons, it may be advantageous for a mobile device to be able to determine its current location. For example, some mobile devices execute applications, such as calendars, reminders, navigation assistants and communication tools, having functionality that may be altered or enhanced depending upon the location of the mobile device.
In instances in which the mobile device is outdoors, the mobile device may interact with the global positioning system (GPS) infrastructure to identify its location. The GPS infrastructure includes a constellation of satellites and ground tracking stations and depends upon published updates of satellite ephemerides. In order to determine its position, a mobile device may include a GPS receiver having a radio for receiving GPS satellite transmissions as well as sufficient computation and storage resources to estimate its geo-referenced latitude, longitude and elevation (LLE). The LLE of a mobile device may be more easily viewed in the context of a map.
However, GPS is generally only effective outdoors such that a mobile device cannot rely upon the GPS infrastructure to determine its location in an indoor setting. As such, various techniques have been developed to permit mobile devices to determine their location indoors. These techniques provide different design tradeoffs regarding the installation and maintenance burden, accuracy, precision, latency, user privacy and device requirements.
For example, some location information can be obtained through dead-reckoning using odometry, pedometry and/or inertial sensing. However, dead-reckoning generally requires initialization from an external data source and calibrated, dedicated hardware. Moreover, techniques reliant upon dead-reckoning can incur position errors that grow without bound and may therefore be unsuitable for applications that require location data over arbitrarily long time scales.
Another technique that may permit location determination in an indoor setting utilizes a dedicated infrastructure, such as passive or active fiducial markers or beacons, along with corresponding hardware onboard the mobile device to support location discovery. These systems can rely on active clients whose motion is tracked and relayed by the infrastructure to other clients, or active infrastructure, from which each client can compute its own location. The dedicated infrastructure may include ultrasound devices, modulated light fixtures, cameras and/or RF sources that are dedicated to location determination applications. As a result of the dedication of this infrastructure to location determination, the infrastructure may impose a deployment burden that may be unacceptable or impractical in some settings.
In order to avoid the issues associated with a dedicated infrastructure, another technique for determining the location of a mobile device in an indoor setting relies upon the radio frequency (RF) signature that is generated by existing RF signal sources that have been deployed for other purposes and is detected by the mobile device at its current location. The RF signals that constitute the RF signatures may be provided by a variety of existing RF signal sources, such as the access points for wireless local area networks (WLANs), cellular networks, Bluetooth or other proximity-based networks or the like. RF signatures generally include the identity of each RF source and the signal strength of the ambient RF signals from each RF source.
However, prior to use of an RF signature-based technique, a survey of the indoor space must be conducted. This initial site survey generally requires skilled technicians to move throughout the space and to identify the RF signatures at each of a plurality of locations within the space and to associate a particular location with each RF signature. Based upon the database of RF signatures and associated locations created by the site survey, mobile devices may thereafter identify their location by determining the RF signature that exists at its current location and then comparing the current RF signature to the database of previously observed RF signatures created by the initial site survey. The mobile device can then identify the previously observed RF signature that most closely matches the current RF signature with the current location of the mobile device then being defined as the location associated with the most closely matching previously observed RF signature.
Unfortunately, the initial site survey that is required prior to use of this technique is a time intensive process that requires the services of one or more skilled technicians. Not only may the initial site survey be labor intensive and, consequently, relatively expensive, but the initial site survey depends upon the skilled technicians being able to access all of the spaces of interest within a building. Because of privacy and/or security issues, it may not always be desirable for a technician to access each of these spaces. Additionally, changes may occur that may render the initial site survey at least partially inaccurate and may necessitate another site survey, at least of a portion of a building, prior to continued reliance upon this location discovery technique. For example, the RF signal sources may change, such as through the addition of another RF signal source or the removal or movement of an existing RF signal source, or the building may be reconfigured, such as by the addition or removal of a wall.
As such, it may be desirable to provide an improved technique for permitting location discovery, such as location discovery by a mobile device in an indoor environment.